Spinal muscular atrophy (SMA): an overview and more

Spinal muscular atrophy (SMA) is a rare genetic disorder that affects the control nerves that branch from the spinal cord above the voluntary muscles. SMA mainly affects children.

A child with SMA has impairments in important functions such as breathing , sucking, and swallowing. Additional conditions may develop as a result of such a violation. For example, weak back muscles can develop abnormal curvatures of the spine , making it difficult to breathe due to compression of the lungs.

Before the advent of feeding tubes, interruption of swallowing used to be fatal in SMA type 1 (the most severe form). There are many assistive devices now available to help children with SMA stay alive (and comfortable, at least compared to previous years).

However, there are still risks. One suffocates. Possibly choking because a child with SMA has weak muscles for swallowing and chewing. Another risk is inhalation or inhalation of food. Aspiration can block the airways and can also be a source of infection.

SMA manifests itself in different ways depending on the type. With all types of SMA, you can expect muscle weakness, wasting, and atrophy, as well as problems with muscle coordination. The reason for this lies in the nature of the disease itself: SMA affects the nervous control of voluntary muscles.

There is no cure for SMA. The most promising prediction comes with early detection. Medical advances can help manage complications associated with SMA.

Types of spinal muscular atrophy

Spinal muscular atrophy affects 1 in 6,000 newborns. It is the leading genetic cause of death in children under 2 years of age. SMA does not require discrimination against those affected.

There are several types of SMA, depending on the degree of SMN protein dysfunction. There are also some types of SMA that are related to other genetic problems.

SMA is classified according to the severity and age of onset of symptoms. Severity, the amount of protein deficiency in motor neurons, and the (early) age of onset tend to correlate with each other. The development of sensation and mind in SMA is completely normal.

Type 1

SMA type 1 is the most serious disease affecting children under 2 years of age. SMA type 1 is usually diagnosed within the first six months of life.

Babies with SMA type 1 may never achieve normal motor development, such as sucking, swallowing, rolling, sitting, and crawling. Children with SMA type 1 usually die before the age of 2, usually from breathing problems.

Babies with SMA type 1 are often lethargic, immobile, and even lethargic. Their tongues move like worms and they cannot hold their heads when sitting.

They may also have noticeable deformities such as scoliosis and muscle weakness, especially in the proximal muscles near the spine.

Type 2

SMA type 2, also called intermediate SMA, is the most common type of SMA. Respiratory infection is the most common cause of death in type 2. However, children with type 2 diabetes can have a normal life expectancy.

SMA type 2 begins between 6 and 18 months or after the child has shown that he can sit without support (after being placed in a sitting position). Type 2 symptoms include deformity, motor retardation, enlarged calf muscles, and tremors in the toes.

First, the proximal muscles located closer to the spine are affected; the legs will weaken in front of the hands. Children with SMA type 2 will never be able to walk without help. The good news is that a child with SMA is more likely to be able to perform tasks with their hands and arms, such as typing, feeding, etc.

Children with SMA type 2 have been found to be very intelligent. Physical therapy, assistive devices, and power wheelchairs can go a long way toward achieving a meaningful life for them.

The two main problems with SMA Type 2 include:

  • Weak respiratory muscles that cause infection
  • Scoliosis and / or kyphosis due to weak muscles in the spine.

Types 3 and 4

Type 3 SMA, also known as mild SMA, begins after 18 months. People with SMA type 3 are often dependent on assistive devices and need constant monitoring of where they are throughout their lives because of the risk of curvature of the airways and spine. They often stop walking for a time in their lives. When they stop walking, it goes from adolescence to 40 years.

While children with SMA type 3 can move and walk, muscle weakness and atrophy of the proximal muscles, that is, those closest to the spine, are observed.

There is a fourth type of SMA, SMA in adults. Type 4 usually appears when a person is 30 years old. As you may have guessed, SMA type 4 is the mildest form on the severity continuum of the disease. Type 4 symptoms are very similar to type 3 symptoms.


SMA is a genetic disorder in which a gene that codes for a muscle protein called SMN (survival motor neuron) does not work properly. SMN protein dysfunction leads to the problems seen in SMA.

SMA is inherited in a recessive manner. This means that for SMA to occur, a child must inherit the defective gene from both parents, and therefore both parents must be carriers of the defective gene. It is estimated that about 1 in 40 people carry this gene. If both parents are carriers, there is a one in four chance that their child will have SMA.

In some people with SMA, other genes may partially compensate for the one that makes faulty SMN proteins. As a result, the severity of SMA varies from person to person.


The first step in obtaining a diagnosis is for a parent or guardian to notice the symptoms of SMA in their child, as explained in this article. The doctor should take a detailed medical history of the child, including a family history and physical exam.

Several types of tests are used to diagnose SMA:

  • Blood test
  • Muscle biopsy
  • Genetic testing
  • EMG

There are many problems with testing for SMA in children, as well as testing that parents are carriers. In 1997, a DNA test called the quantitative PCR test for the SMN1 gene was released to help parents determine if they carry the mutant gene that causes SMA.

The test is done by taking a blood sample. Assessing the general population is too difficult, which is why it is intended for people with a family history of SMA. The test is possible before birth by amniocentesis or chorionic villus sampling.

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Watch out

The treatment of SMA aims to maintain life, promote independence and / or improve the quality of life of the patient. Some examples of methods of care and treatment include:

  • Physiotherapy
  • Use of assistive devices such as wheelchairs , breathing apparatus, and feeding tubes . (There are many assistive devices for SMA. It is best to discuss this with your therapy team.)
  • Spinal deformity surgery

Doctors recommend that families work with the medical team using an interdisciplinary approach. A patient with SMA should receive frequent medical examinations throughout his life. Genetic counseling for family members is very important.

Activity should not be avoided, but used in a way that prevents deformation, contracture, and stiffness, and maintains range of motion and flexibility. Therefore, one should not do this to the point of exhaustion. Good nutrition will allow the patient to use his muscles as well.

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